Projection screen and manufacturing method thereof

ABSTRACT

A projection screen and a method for manufacturing the same providing clear images regardless of the brightness of the environment where the projection screen is used.  
     A projection screen according to the present invention is a projection screen ( 1 ) for displaying an image by projecting light from a light source ( 11 ). The projection screen ( 1 ) includes an optical thin film ( 3 ) composed of dielectric multilayers having high reflectance for light in particular wavelength ranges and high transmittance for at least visible light except the light in the particular wavelength ranges. The thickness of each of the dielectric multilayers composing the optical thin film ( 3 ) is determined by simulation based on a matrix method. With the thus constructed projection screen of the invention, the optical thin film ( 3 ) serves as so-called a band-pass filter. More specifically, the optical thin film ( 3 ) functions as a band-pass filter which reflects light of the particular wavelengths and substantially transmits the light except the light of the particular wavelengths, thereby separating incident light.

TECHNICAL FIELD

[0001] The present invention relates to projection screens, moreparticularly to a projection screen which enables an image of projectedlight from a projector to be well perceived even in a brightenvironment.

BACKGROUND ART

[0002] These days, overhead projectors and slide projectors are widelyused when speakers present their materials in conferences or the like.Video projectors and motion film projectors employing liquid crystaldisplays are also becoming popular for home applications. Typically,these projectors optically modulate light from light sources viatransparent liquid crystal display panels into image-forming light andemit this image-forming light through optical systems such as lenses,thereby projecting the emitted image-forming light onto screens.

[0003] For example, a front projector which can form color images on ascreen includes an illumination optical system which separates a lightbeam emitted from a light source into light components for red (R),green (G), and blue (B) and combines each light component on apredetermined optical path; a liquid crystal display panel (light valve)which optically modulates each light component for red, green, and bluethat is separated by the illumination optical system; and alight-combining unit which combines the light components for red, greenand blue that are optically modulated by the liquid crystal displaypanel. The front projector magnifies the color image composed by thelight-combining unit to project it onto a screen via a projection lens.

[0004] Furthermore, projectors that spatially modulate each lightcomponent for red, green and blue using a narrow-band,three-primary-color light source as a light source, and a grating lightvalve (GLV) in place of the liquid crystal display panel are also beingdeveloped these days.

[0005] Incidentally, the above-described projectors employ projectionscreens to project images. These projection screens are broadly dividedinto a transmissive type in which light is emitted from behind thescreen to project an image onto the screen, and a reflective type inwhich light is projected from the front onto the screen to reflect animage. With either type, bright and high-contrast images are necessaryfor the screen to provide excellent visibility.

[0006] However, unlike self-luminescent displays and rear projectors,the front projector described above exhibits a problem in that it cannotreduce reflection of extraneous light with, e.g., an ND filter, wherebyenhancement of the luminous contrast on the screen is difficult.

[0007] To address this problem, in Japanese Patent No. 2889153, as shownin FIG. 10, a transparent layer 102 is formed on a diffusion layer 101and protrusions 103 are formed on the surface of the transparent layer102. Opaque layers 104 are formed by applying black-coating only on theside walls of the protrusions 103. The provision of these opaque layers104 lowers the black level, leading to an enhancement in brightness andcontrast. However, pattern formation and partial coating require timeand work. Furthermore, although screens should preferably be flexiblefor easy storage, this screen has no flexibility. Moreover, JapanesePatent No. 3103802 discloses an example of a flexible screen as shown inFIG. 11. With this screen, all of a supporting member 201, a reflectivelayer 202, a light absorption layer 203, and a diffusion layer 204composing the screen are flexible, thereby imparting flexibility to thescreen itself. However, the light absorption layer is disposed closer tothe surface of the screen than the reflective layer so that the lightabsorption layer absorbs even the light intended to be reflected,resulting in a lower white level.

[0008] The projectors described above reflect projected light that hasbeen subjected to image processing onto the screen, and the imagecontrast greatly depends on the brightness of the surroundings. Simplyincreasing the reflectance of the screen allows not only the projectedlight but also the extraneous light to be well reflected, resulting indeterioration of the perceived image. Hence, it is difficult to obtain aclear image in a bright environment.

[0009] The present invention aims to solve the aforementioned problemsand it is an object of the present invention to provide a clear imageregardless of the brightness of the environment where a projectionscreen is used.

DISCLOSURE OF INVENTION

[0010] In order to attain the above-described object, a projectionscreen of the present invention displays an image by projecting lightfrom a light source. This projection screen includes an optical thinfilm composed of dielectric multilayers that have high reflectance forlight in particular wavelength ranges and high transmittance for atleast visible light outside of the particular wavelength ranges. Thethickness of each of the dielectric multilayers composing the opticalthin film is determined by simulation based on a matrix method.

[0011] With the projection screen of the present invention constructedas described above, the optical thin film functions as so-called aband-pass filer. That is, the optical thin film functions as a band-passfiler that reflects light in particular wavelength ranges andsubstantially transmits light of wavelengths excluding these particularwavelengths, thereby separating incident light.

[0012] Due to this optical thin film, the projection screen reflectsmost of the light in the particular wavelength ranges. On the otherhand, if incidence of extraneous light takes place, the projectionscreen hardly reflects the extraneous light but transmits most of it.

[0013] Accordingly, the projection screen of the present invention canselectively reflect light in the particular wavelengths and suppressreflection of extraneous light as compared to ordinary screens. Thus,the low contrast of an image formed on the projection screen is improvedand reflection of extraneous light is effectively reduced, resulting inbright images. Even if the projection screen is used in a brightenvironment, it can provide clear images regardless of the brightness ofthe environment where the projection screen is used.

[0014] Designing of the optical thin film is a critical factor toachieve the aforementioned functions. For example, the optical thin filmis composed of dielectric multilayers where high-refraction layers andlow-refraction layers are alternately laminated. Each of the dielectricmultilayers is designed by simulation based on a matrix method such thatthe optical thin film reflects light in particular wavelength ranges andsubstantially transmits light except the light in the particularwavelength ranges, thereby obtaining the above-mentioned effects.

[0015] When the optical thin film is designed by the simulation based onthe matrix method so as to reflect the light in the particularwavelength ranges and substantially transmit light except the light inthe particular wavelength ranges, a reflective band for the particularwavelengths is formed by the optical thin film. Hence, the optical thinfilm exhibits high reflectance for the particular wavelengths and hightransmittance for the visible light of wavelengths not including theparticular wavelengths.

[0016] Accordingly, with selection of a red wavelength, a greenwavelength and a blue wavelength as the particular wavelengths, theoptical thin film is designed by simulation based on the matrix methodso as to reflect light in the particular wavelength ranges andsubstantially transmit light outside of the particular wavelengthranges, whereby the reflective band for the wavelength ranges is formedby the optical thin film. Hence, the optical thin film is constructed toexhibit high reflectance for these wavelengths and to exhibit hightransmittance for the visible light of wavelengths not including theparticular wavelengths.

[0017] The projection screen according to the present invention, besidesincluding the optical thin film, which functions as a band-pass filter,preferably includes a light diffusion layer on the outermost layer ofthe optical thin film or in the optical thin film as an interlayer. Thelight diffusion layer diffuses the light reflected by the optical thinfilm to generate diffused light. Without the provision of the lightdiffusion layer, a viewer perceives only a specular reflection componentas a reflected light from the projection screen. When the reflectedlight is composed of only the specular reflection component, there aredisadvantages for the viewer such as an unclear image and a limitedfield of view. On the other hand, the light diffusion layer enables theviewer to perceive the diffused light, thereby greatly improving a fieldof view. Accordingly, the viewer can enjoy natural images.

[0018] Furthermore, in order to attain the above-described object, witha method for manufacturing a projection screen according to the presentinvention, a projection screen includes an optical thin film composed ofdielectric multilayers and displays an image by projecting light from alight source. The thickness of each of the dielectric multilayers isdetermined by simulation based on a matrix method so as to have highreflectance for light in particular wavelength ranges and to have hightransmittance for at least visible light outside of the particularwavelength ranges.

[0019] With the method for manufacturing a projection screen accordingto the above-described present invention, the thickness of each of thedielectric multilayers is determined by simulation based on the matrixmethod so that the optical thin film functioning as so-called aband-pass filter is formed. That is, manufactured is the optical thinfilm functioning as a band-pass filter that reflects light in theparticular wavelength ranges and substantially transmits the light ofthe wavelengths except the particular wavelengths, thereby separatingincident light.

[0020] The projection screen having the thus constructed optical thinfilm reflects most of the light in the particular wavelength ranges. Onthe other hand, if incidence of extraneous light takes place, theprojection screen hardly reflects the extraneous light but transmitsmost of it.

[0021] Accordingly, this projection screen can selectively reflect thelight of the particular wavelengths and thus can suppress projection ofextraneous light as compared to ordinary screens. Hence, low contrast ofan image formed on the projection screen is improved and projection ofextraneous light is effectively reduced, thereby providing brightimages. Thus, with the method for manufacturing a projection screenaccording to the present invention, manufactured is a projection screenwhich can provide clear images regardless of the brightness of theenvironment where the projection screen is used, even in a brightenvironment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a cross-sectional view of an exemplary structure of aprojection screen according to the present invention;

[0023]FIG. 2 is a schematic view of a multilayer film;

[0024]FIG. 3 is a schematic view of the structure of a gratingprojector;

[0025]FIG. 4 is a conceptual view of a state of light incident on a GLV;

[0026]FIG. 5 is a conceptual view of a state of a light reflected by theGLV;

[0027]FIG. 6 is a plan view of an exemplary structure of the GLV;

[0028]FIG. 7 is a cross-sectional view of another exemplary structure ofthe projection screen according to the present invention;

[0029]FIG. 8 is a cross-sectional view of the projection screenaccording to an example;

[0030]FIG. 9 is a characteristic view showing a relationship between thewavelength and reflectance of the projection screen according to theexample;

[0031]FIG. 10 is a sectional view of an exemplary structure of aconventional screen; and

[0032]FIG. 11 is a sectional view of an exemplary structure of anotherconventional screen.

BEST MODE FOR CARRYING OUT THE INVENTION

[0033] The present invention will now be described with reference to thedrawings. The present invention is not restricted to the followingdescription and may be modified within the scope of the presentinvention.

[0034] A projection screen according to the present invention displaysan image by projecting light from a light source. This projection screenincludes an optical thin film composed of dielectric multilayers havinghigh reflectance for light in particular wavelength ranges and hightransmittance for at least visible light other than the light in theparticular wavelength ranges. The thickness of each of the dielectricmultilayers composing the optical thin film is determined by simulationbased on a matrix method.

[0035]FIG. 1 shows a cross-sectional view of a screen for a frontprojector according to the present invention. A projection screen 1displays an image from a grating projector having a grating light valve(referred to as a GLV hereinbelow). The projection screen 1 displays animage by projecting three-primary-color light emitted from athree-primary-color light source, which is a light source for thegrating projector. The projection screen 1 includes an optical thin film3 on a screen substrate 2, the optical thin film 3 having dielectricmultilayers serving as a band-pass filter. A light diffusion layer 4 isdisposed on the optical thin film 3, and a protective film 5 is formedon top of the light diffusion layer 4.

[0036] The screen substrate 2 functions as a support for the projectionscreen 1 and may be composed of a polymer, i.e., poly(ethyleneterephthalate) (PET), poly(ethylene naphthalate) (PEN), poly(ethersulfone) (PES), or polyolefin (PO). The screen substrate 2 containsblack paint or the like and thus is black. The black screen substrate 2functions as a light absorption layer. Therefore, as will be describedbelow, the screen substrate 2 absorbs light from the optical thin film3, suppressing reflection of the light from the optical thin film 3.Accordingly, only the three-primary-color light is obtained as reflectedlight, leading to an enhancement in black level and an improvement incontrast.

[0037] Instead of the above screen substrate 2, the surface of a screensubstrate may be black-coated. In such a case, the black coating,serving as the light absorption layer, does not reflect but absorbs thelight from the optical thin film 3, causing an enhanced black level andan improved contrast. As described above, since the light absorptionlayer is formed not on the optical thin film 3 but on the surface of thescreen substrate 2, light other than the three-primary-color light iseffectively absorbed without absorption of light necessary forprojection. In FIG. 1, the screen substrate 2 is composed of black PETand thus functions as both the support and the light diffusion layer.

[0038] Furthermore, the screen substrate 2 is composed of a flexiblematerial, thereby imparting flexibility to the projection screen 1 andthus achieving the flexible projection screen 1.

[0039] The optical thin film 3 is composed of dielectric multilayerswhere high-refraction layers H and low-refraction layers L arealternately laminated. The high-refraction layers H are dielectric filmscomposed of a high-refraction material, while the low-refraction layersL are dielectric films composed of a low-refraction material. Thethickness of each of the dielectric multilayers is determined bysimulation based on a matrix method such that the optical thin filmexhibits high reflectance for light in particular wavelength ranges andhigh transmittance for at least visible light excluding the light in theparticular wavelength ranges.

[0040] The projection screen 1 includes the optical thin film 3 wherehigh-refraction layers H1-H51 and low-refraction layers L1-L50 arealternately laminated, as shown in FIG. 1. A red wavelength, a greenwavelength and a blue wavelength are selected as the particularwavelengths, and with the use of the simulation based on the matrixmethod, the high-refraction layers H1-H51 and the low-refraction layersL1-L50 are designed to show high reflectance for light of the red, greenand blue wavelengths and to show high transmittance for at least visiblelight excluding the light of the red, green, and blue wavelengths.

[0041] The theory of film designing by the simulation based on thematrix method will now be briefly described. Referring to FIG. 2, amultilayer optical thin film is composed of a number of differentmaterials and in this optical thin film, multiple reflection occurs atinterfaces between these layers, for example. Incidence of light on thisoptical thin film at an angle of θ₀ will cause the light to become inphase depending on the type and wavelength of the light source and onthe optical thickness of each layer (the product of a refractive indexand a geometric thickness), and thus the reflected light beams may showcoherence, interfering with each other. This is the principal of filmdesigning. Typically an interference filter will now be described.

[0042] Referring to FIG. 2, the optical thin film is composed of Llayers represented by j=1,2,3, . . . , (L−1), L, and each layer has arefractive index n_(j) and a geometric film thickness d_(j). Amultilayer film is formed on a substrate with a refractive index n_(s),and light with a wavelength λ is incident on the top of the multilayerfilm from a medium (in most cases, air n_(m)=1.00) at an angle of θ₀. Asshown in the drawing, the incident angle of each layer is θ_(j). Theplane of polarization of the incident light is determined separately.

[0043] The transmittance T and the reflectance R are calculated from theabove-described values by a matrix method taking into considerationwhether or not Maxwell's equations satisfy the following conditions atthe interfaces of layers.

[0044] Assuming that the film surface is semi-infinite, the amplitudereflection coefficient r and the transmittance coefficient t for themultilayers L are given by the following equations (1) and (2):$\begin{matrix}{r = \frac{{\eta_{m}E_{m}} - H_{m}}{{\eta_{m}E_{m}} + H_{m}}} & (1) \\{t = \frac{2\quad \eta_{m}}{{\eta_{m}E_{m}} + H_{m}}} & (2)\end{matrix}$

[0045] where E_(m) and H_(m) are electric field and magnetic fieldvectors, respectively, represented by the following equation (3):$\begin{matrix}{\begin{pmatrix}E_{m} \\H_{m}\end{pmatrix} = {M\begin{pmatrix}1 \\\eta_{s}\end{pmatrix}}} & (3)\end{matrix}$

[0046] where M is a matrix product represented by the following equation(4):

M=M _(L) M _(L−1) . . . M _(j) . . . M ₂ M ₁  (4)

[0047] where M is a 2 by 2 matrix and thus M_(j) denotes the j-th matrixof the film represented by the following equation (5): $\begin{matrix}{M_{j} = {\begin{pmatrix}m_{11} & {\quad m_{12}} \\{\quad m_{21}} & m_{22}\end{pmatrix} = \begin{pmatrix}{\cos \quad \delta_{j}} & {{{/\eta_{j}} \cdot \sin}\quad \delta_{j}} \\{{ \cdot \eta_{j}}\quad \sin \quad \delta_{j}} & {\cos \quad \delta_{j}}\end{pmatrix}}} & (5)\end{matrix}$

[0048] where η_(j) is given by the following equation (6):

δ_(j)=(2π/λ)(n _(j) d _(j) cos θ_(j))  (6)

[0049] In equation (6), n_(j)d_(j) cos θ_(j) represents the effectiveoptical thickness of the j-th layer with the refractive index θ_(j) andin equations (1) to (6), each η represents the effective refractiveindex of the medium, the substrate, or each layer, and is given by thefollowing equation (7), according to parallel (p) or perpendicular (s)light incident on the surface: $\begin{matrix}{\eta = \{ \begin{matrix}{{n/\cos}\quad {\theta ( {p\text{-}{POLARIZATION}} )}} \\{n\quad \cos \quad {\theta ( {s\text{-}{POLARIZATION}} )}}\end{matrix} } & (7)\end{matrix}$

[0050] The angle θ_(j) is equal to the incident angle θ₀ at the mediumfrom which light is incident, according to Snell's law which isexpressed by the following equation (8):

n _(m) sin θ₀ =n _(j) sin θ_(j)  (8)

[0051] The transmittance and intensity of the reflected light are givenby the following equations (9) and (10), and the phase change ∈_(T) and∈_(R) in transmittance and reflection are given by the followingequations (11) and (12), respectively:

T=(η_(s)/η_(m))|t| ²  (9)

R=|r| ²  (10)

∈_(T)=arg r  (12)

∈_(R)=arg r  (12)

[0052] In the above description, it is implied that absorption in allthe multilayers is negligible and thus T+R=1. However, in a case whereany layer absorbs light, the refractive index must be replaced by thecomplex refractive index represented by the following equation (13):

ñ=n−ik  (13)

[0053] In equation (13), k is an extinction coefficient of the film.Even when a matrix is a complex number, the determinant remains one.Therefore, the absorption coefficient A is determined by the followingequation (14):

A=1−T−R  (14)

[0054] Furthermore, when the polarization of the incident light randomlychanges, T and R are given by the following equations (15) and (16):

T=½(T _(P) +T _(S))  (15)

R=½(R _(P) +R _(S))  (16)

[0055] The simulation based on the above equations determines thecharacteristics of the optical thin film. According to the presentinvention, the thickness of the optical thin film 3 with desirablecharacteristics is calculated by the simulation based on theseequations.

[0056] When the optical thin film 3 is designed to have a thickness bythe simulation based on the matrix method to exhibit high reflectancefor light in particular wavelength ranges and to exhibit hightransmittance for at least visible light outside of the particularwavelength ranges, that is, when the thickness of the optical thin film3 is determined so as to reflect the light in the particular wavelengthranges and to substantially transmit the light outside of the particularwavelength ranges, a reflective band for the particular wavelengths isformed by the optical thin film. Due to the formation of this reflectiveband, the optical thin film 3 reflects the three-primary-color lightemitted from the light source without transmitting it. The optical thinfilm 3 transmits light in the wavelength ranges outside the reflectiveband. Thus, functioning as a band-pass filter for the wavelength rangesof the three primary colors, the optical thin film 3 selectivelyreflects the three-primary-color light, and selectively transmits thelight in the wavelength ranges excluding the three-primary-color light.Consequently, the optical thin film 3 exhibits high reflectance for theparticular wavelengths while exhibiting high transmittance for thevisible light except the particular wavelengths.

[0057] Thus, the wavelengths for red, green, and blue are selected asthe particular wavelengths. The thickness of the optical thin film isdetermined by the simulation based on the matrix method such that theoptical thin film reflects the light of the red, green, and bluewavelengths, and substantially transmits the light of wavelengths notincluding these red, green, and blue wavelengths. Thus, the reflectiveband for these wavelengths is formed by the optical thin film 3. Hence,the optical thin film exhibits high reflectance for thethree-primary-color light while exhibiting high transmittance for thevisible light not including the three-primary-color light.

[0058] According to the present invention, it may be possible to designthe optical thin film 3 to reflect light of certain narrow wavelengthranges within the wavelength ranges for red, green and blue or lightwith somewhat broader wavelength ranges. The particular wavelengthranges are not limited to the wavelengths for red, green and blue, andother wavelength ranges may also be used. Furthermore, the number of theparticular wavelength ranges is not limited to three but may be one ormore than three.

[0059] In other words, according to the present invention, since thethickness of the optical thin film 3 is determined by the simulationbased on the matrix method, the wavelength range for the reflective bandin the optical thin film 3 and the number of wavelength ranges may befreely determined. Thus, the optical thin film 3 with desiredcharacteristics can be obtained due to the very high design freedom inthe optical characteristics of the optical thin film 3.

[0060] Accordingly, with the projection screen 1, the red, green, andblue wavelengths are selected as the particular wavelengths, and theoptical thin film 3 is designed by the simulation based on the matrixmethod to reflect the light of the red, green and blue wavelengths andto substantially transmit light of the wavelengths except the red, greenand blue wavelengths. The three-primary-color light emitted from thethree-primary-color light source is selectively reflected and the lightexcept the three-primary-color light is selectively transmitted. Thelight passing through such an optical thin film 3 is not reflected bythe screen substrate 2, which functions as the light absorption layerdescribed above, but is absorbed in the screen substrate 2, so that thethree-primary-color light reflected off the reflective band can beextracted as reflected light.

[0061] Thus, with the projection screen 1, even if extraneous lightreaches the projection screen 1, the light except thethree-primary-color light is eliminated by passing through the opticalthin film, thereby preventing disadvantages caused by extraneous lightsuch as low contrast and projection of extraneous light.

[0062] That is, the projection screen 1 selectively reflects thethree-primary-color light and suppresses reflection of extraneous lightas compared to ordinary screens, thereby achieving improved contrast ofimages on the projection screen 1 and effectively reducing projection ofextraneous light, resulting in bright images. Accordingly, thisprojection screen 1 can project a clear image regardless of theenvironment where the projection screen is used, even in brightsurroundings.

[0063] As described above, when the emitted light from thethree-primary-color light source in the projector has steeper wavelengthcharacteristics, by the synergistic effect with the above-describedaction of the optical thin film 3, the light reflected by the screen issubstantially the same as the light emitted from the projector, thusenhancing the advantages of the present invention. Thethree-primary-color light source is preferably a light source whichemits light with a wavelength distribution of several nanometers, suchas laser light.

[0064] As described, although laser light is preferred as the lightsource, a light emitting device such as a light emitting diode with arelatively broad wavelength range may also be used, for example. A lightsource with a broader wavelength distribution may further be used alongwith a filter, a nonlinear optical device, or a nonlinear optical thinfilm to separate the visible light range into three primary colors bywavelength.

[0065] The high-refraction layer H may be composed of a high-refractionmaterial such as niobium pentoxide (Nb₂O₅), titanium dioxide (TiO₂), andtantalum pentoxide (Ta₂O₅). The low-refraction layer L may be composedof a low-refraction material such as silicon dioxide (SiO₂) andmagnesium fluoride (MgF₂). According to the present invention, however,the material for the high-refraction layer H is not limited to the onesabove, and materials of a refractive index ranging from about 2.0 to 2.6may preferably be used. Similarly, the material for the low-refractionmaterial L is not limited to the ones above, and materials of arefractive index ranging from about 1.3 to 1.5 may be preferably used.

[0066] Furthermore, the thickness of the dielectric multilayerscomposing the optical thin film 3, namely, the thickness of each of thehigh-refraction layer H and the low-refraction layer L preferably rangesfrom about 5 nm to 100 nm. Due to the lamination of the high-refractionlayers H and the low-refraction layers L with such thicknesses, theoptical thin film 3 reliably functions as a band-pass filter for thewavelengths of three primary colors.

[0067] Moreover, the number of dielectric multilayers composing theoptical thin film 3 is not specifically limited and may be determined asdesired, for example, one hundred and one layers as shown in FIG. 1.Preferably, the dielectric multilayers are constructed such that theoutermost layer on which the narrow-band, three-primary-color light isincident and the other outermost layer are composed of thehigh-refraction layer and thus the total number of layers is odd. Thedielectric multilayers, namely, the optical thin film 3 composed of odddielectric films functions better than that composed of even dielectricfilms as a band-pass filter for the wavelengths of three primary colors.

[0068] Specifically, the sum of the high-refraction layers H and thelow-refraction layers L is preferably about 50 to 100 layers. If thenumber of layers is too small, the optical thin film 3 may not be ableto sufficiently serve as a band-pass filter for the wavelengths of threeprimary colors. If the number of layers is too large, it takes a longtime to manufacture the optical thin film 3. Accordingly, the sum of thehigh-refraction layers H and the low-refraction layers L is about 50 to100 layers so that the optical thin film 3 sufficiently functions as aband-pass filter for the wavelengths of the three primary colors, andthus the optical thin film 3 is efficiently constructed.

[0069] As shown in FIG. 1, the projection screen 1 includes a lightdiffusion layer 4 on the optical thin film 3. The light diffusion layer4 diffuses the light reflected by the optical thin film 3 to generatediffused light. The projection screen 1 reflects the three-primary-colorlight thanks to the provision of the optical thin film 3 so that aviewer perceives the reflected image of the image projected on theprojection screen 1, namely, the reflected light of the image projectedon the projection screen 1. However, when the reflected light on thescreen is composed of a specular reflection component, there areproblems for the viewer such as an unclear image and a limited field ofview. That is, the viewer cannot perceive natural images.

[0070] To this end, the light diffusion layer 4 is provided in theprojection screen 1, enabling a diffusive reflection component from theprojection screen to be perceived. As shown in FIG. 1, provision of thelight diffusion layer 4 on the optical thin film 3 permits the lightwhich has passed through the light diffusion layer 4 and been reflectedby the optical thin film 3 to pass through the light diffusion layer 4one more time. At this time, the light reflected by the optical thinfilm 3 is diffused through the light diffusion layer 4, therebyobtaining the diffusive reflection component excluding a specularreflection component. The reflected light from the projection screen 1is composed of the specular reflection component and the diffusivereflection component so that the viewer can perceive the diffusivereflection component in addition to a specular reflection component,resulting in a great improvement in the field of view. Hence, the viewercan enjoy natural images.

[0071] The diffusive reflection component is diffused light that hasbeen reflected by the optical thin film 3. The optical thin film 3reflects light of predetermined wavelengths, i.e., thethree-primary-color light, so naturally the diffusive reflectioncomponent is also the three-primary-color light. Accordingly, even ifextraneous light enters the projection screen 1, the light other thanthe three-primary-color light will not constitute the diffusivereflection component. Hence, the light diffusion layer 4 suppresses lowcontrast and projection of the extraneous light, leading to a preferablefield of view.

[0072] The light diffusion layer 4 is not specifically limited and anyknown diffusion layer may be used. For example, as shown in FIG. 1, thelayer may be composed of arrayed beads. The light diffusion layer 4composed of the arrayed beads may exhibit excellent light diffusioncharacteristics for light of a particular wavelength range by alteringvarious conditions such as the type or size of the beads employed. Thatis, provision of such a light diffusion layer causes a projection screento exhibit excellent light diffusion characteristics exclusively for thelight of a particular wavelength range. Alternatively, a microlens array(MLA) film may be used as the light diffusion layer 4.

[0073] The above-described light diffusion layer 4 may be composed ofone layer or several layers depending on the application of theprojection screen. The light diffusion layer 4 may be disposed on theoptical thin film 3, namely, on the topmost layer of the dielectricmultilayers or in the optical thin film 3 as an interlayer. In eitherway, the same effects described above can be achieved.

[0074] A protective film 5 protects the optical thin film 3 and thelight diffusion layer 4 from the exterior and has no optical function asa band-pass filter. Assuming that materials composing the optical thinfilm 3 and the light diffusion layer 4 are sensitive to moisture and theprojection screen is used in a very humid environment or exposed towater, the optical thin film 3 might deteriorate, resulting in lowerdurability and compromised quality. Furthermore, a graze or scratch dueto external factors might also deteriorate its durability or quality.Thus, the protective film 5 protects the optical thin film 3 and thelight diffusion layer 4, providing a durable, high-quality projectionscreen.

[0075] The above-described projection screen 1 may be manufactured asfollows.

[0076] First, the screen substrate 2 composed of black PET is preparedas the screen substrate and the optical thin film 3 constituted of thedielectric multilayers is formed on one surface of the screen substrate2.

[0077] The optical thin film 3 is composed of the dielectricmultilayers. Specifically, as shown in FIG. 1, the high-refractionlayers H1-H51, which are dielectric films composed of a high-refractionmaterial, and the low-refraction layers L1-L50, which are dielectricfilms composed of a low-refraction material, are alternately laminatedby AC sputtering to form a total of one hundred and one laminated layersof the optical thin film 3. At this time, the optical thin film 3 isformed such that its thickness is determined by the simulation based onthe matrix method in order for the optical thin film to have highreflectance for the wavelength ranges for the three primary colors,namely, the wavelength ranges for blue, green and red, and to have hightransmittance, i.e., low reflectance for wavelength ranges other thanthese wavelength ranges for the three primary colors, and then thethickness of each high-refraction layer H and low-refraction layer L isdetermined.

[0078] Next, on the resultant optical thin film 3, the light diffusionlayer 4 composed of arrayed beads with a predetermined size is formed,and the protective film 5 is formed on top of the light diffusion layer4, thereby completing the projection screen 1. The light diffusion layer4 and the protective film 5 may be formed with any known method.

[0079] A grating projector 11 employing a GLV, which will be describedbelow, may be used as the grating projector.

[0080] As shown in FIG. 3, the grating projector 11 includes a firstlaser oscillator 21 r, a second laser oscillator 21 g, and a third laseroscillator 21 b which are light sources emitting a red light component,a green light component, and a blue light component, respectively. Inthe description below, the first, second, and third laser oscillators 21r, 21 g, and 21 b may be collectively called laser oscillators 21. Thelaser oscillators 21 may be constituted of a semiconductor laser deviceor a solid-state laser device which emits light for each color. Thefirst, second, and third laser oscillators 21 r, 21 g, and 21 b,respectively, emit narrow-band, three-primary-color light; thewavelength of the red laser light component is 642 nm, the wavelength ofthe green laser light component is 532 nm, and the wavelength of theblue laser light component is 457 nm.

[0081] In the grating projector 11, a collimator lens 22 r for the redlaser light component, a collimator lens 22 g for the green laser lightcomponent, and a collimator lens 22 b for the blue laser light componentare provided on the optical axis of each light component emitted fromeach laser oscillator 21. Simply, these collimator lenses arecollectively called collimator lenses 22. Light emitted from the laseroscillators 21 is collimated by the respective collimator lenses 22 tobe incident on a cylindrical lens 23. The cylindrical lens 23 convergesthe incident light on a GLV 24.

[0082] More specifically, the grating projector 11 does not use lightonly from a single light source but includes, as a light source, thelaser oscillators 21 for each of the three colors, each of whichseparately emits light. Furthermore, the grating projector 11 isconstructed such that light emitted from each laser oscillator 21 isincident directly on the cylindrical lens 23 via the collimator lens 22.

[0083] The GLV 24 will now be described. First of all, the principle ofthe GLV will be described. The GLV has, on a substrate, a plurality ofprecision strips formed with the use of semiconductor manufacturingtechnologies. Each strip is freely moved up and down by a piezoelectricdevice or the like. With the thus constructed GLV, each strip is drivenmechanically to change its height and irradiated with light of apredetermined wavelength, thereby constituting a phase grating as awhole. That is, the GLV creates diffracted light of the ±1-st order (orhigher order) by light irradiation.

[0084] Such a GLV is irradiated with light while diffracted light of the0th order is blocked. This allows each strip in the GLV to move up anddown to create or quench diffracted light, thereby displaying an image.

[0085] Various types of display devices which display images utilizingthe aforementioned features of the GLV are proposed. With such displaydevices, in displaying a plane image having display units (referred toas pixels below), one pixel is defined by about six strips. In a groupof strips corresponding to one pixel, adjacent strips are moved up anddown alternately.

[0086] By separately wiring each strip of the GLV to drive themindividually, a desirable one-dimensional phase distribution isgenerated. The thus constituted GLV is regarded as a specularone-dimensional spatial phase modulator.

[0087] When the GLV is constituted as the specular one-dimensionalspatial phase modulator, for example, as shown in FIG. 4, each strip 31of a GLV 31 is separately driven to form a desirable phase distribution.Light of a predetermined wavelength that is in phase relative to the GLV31 is incident on the GLV as indicated by the arrow in FIG. 4, and ismodulated to be reflected, thereby generating a desirableone-dimensional wave front as shown in FIG. 5.

[0088] As shown in FIG. 6, the GLV 24 utilizing such a principleincludes a plurality of fine strips 42 formed on a substrate 41. Eachstrip 42 includes a driver 43 composed of circuitry and wiring fordriving and the driver 43 drives each strip 42 to move up and downrelative to the main surface of the substrate 41.

[0089] With the GLV 24, the strips 42 are arranged one-dimensionally toconstitute a strip row. A plurality of strip rows is disposed for eachwavelength of incident light. Specifically, as typically shown in FIG.6, a red light component, a green light component, and a blue lightcomponent of three-color light are incident on the GLV 24, and at theposition on which these light components are incident, a strip row 44 rfor the red light component, a strip row 44 g for the green lightcomponent, and a strip row 44 b for the blue light component arearranged side by side parallel to each other. Simply, these strip rows44 r, 44 g, and 44 b are collectively called strip rows 44 hereinbelow.

[0090] In the strip rows 44, each strip 42 can be driven separately andthus the strip rows 44 can create a desirable phase distribution, asdescribed with reference to FIG. 4 and FIG. 5. Therefore, with the GLV24, a desirable one-dimensional wave front is separately formed for eachof the incident red light component, green light component, and bluelight component by the respective strip row 44 r for the red lightcomponent, the strip row 44 g for the green light component, and thestrip row 44 b for the blue light component.

[0091] Therefore, with the GLV 24, the incident three-color light isspatially modulated respectively by the strip row 44 r for the red lightcomponent, the strip row 44 g for the green light component, and thestrip row 44 b for the blue light component to be reflected as adesirable one-dimensional wave front. That is, the GLV 24 functions as aspatial modulator in a display device 30.

[0092] The thus constructed GLV 24 is finely produced with semiconductormanufacturing technologies and operated at very high speed. Therefore,the GLV 24 is suitable for the spatial modulator in an image displaydevice, for example. Furthermore, the GLV 24 includes the respectivestrip rows 44 for the wavelength range of each light component to bemodulated and these strip rows 44 are integrally formed with thesubstrate 41. Thus, the image display device employing the GLV 24 as thespatial modulator not only has a low parts count but also does notrequire alignment of strip rows for the wavelength of each lightcomponent.

[0093] In the grating projector 11, light which has been modulated andreflected by the GLV 24 reenters the cylindrical lens 23 to becollimated thereby. A first volume hologram 25 a and a second volumehologram 25 b are disposed on the optical path of the collimated lightby the cylindrical lens 23.

[0094] The first volume hologram 25 a diffracts the red light componentWR and the second volume hologram 25 b diffracts the blue lightcomponent WB in the same direction as the red light component WR isdiffracted. These first and second volume holograms 25 a and 25 b do notdiffract the green light component WG but let it travel straight aheadto be emitted through the holograms in the same direction as the redlight component WR is diffracted. In this way, the three-color lightcomponents diffracted by the GLV 24 are combined to be emitted in afixed direction. That is, in the grating projector 11, the first and thesecond volume holograms 25 a and 25 b constitute a wave-combining unit.

[0095] The light combined by the first and second volume holograms 25 aand 25 b is scanned by a galvano meter mirror 26 in a predetermineddirection and projected via a projection lens 27 onto the projectionscreen 1. Thus, the grating projector 11 displays a color image on theprojection screen 1.

[0096] As is described above, with the projection screen 1 of thepresent invention, the three-primary-color light emitted from thegrating projector 11 passes through the protective film 5 and the lightdiffusion layer 4 to be incident on and reflected by the optical thinfilm 3. Then, this reflected light reenters the light diffusion layer 4to be diffused at a predetermined ratio and this diffusive reflectioncomponent is emitted through the protective film 5. The reflected lightcomponent which is not diffused by the light diffusion layer passesthrough the protective film 5 to be emitted as the specular reflectioncomponent. Accordingly, the reflected light from the projection screen 1is composed of the specular reflection component and the diffusivereflection component, whereby the viewer can perceive not only thespecular reflection component but also the diffusive reflectioncomponent, leading to a great improvement in the field of view. Thus,the viewer can enjoy natural images.

[0097] Furthermore, the specular reflection component and the diffusivereflection component constitute the light reflected off the optical thinfilm 3. The light of predetermined wavelengths, that is, thethree-primary-color light, is reflected by the optical thin film 3 sothat the specular reflection component and the diffusive reflectioncomponent are also three-primary-color light. Accordingly, even thoughextraneous light enters the projection screen 1, light except thethree-primary-color light will not be reflected, thereby effectivelyimproving the low image contrast and projection of extraneous lightcaused by extraneous light, leading to clear images. Hence, theprojection screen 1 can provide clear images regardless of thebrightness of the environment where the projection screen is used, evenin a bright environment.

[0098] Next, a modification of the above-described projection screen 1will now be described. FIG. 7 shows a cross section of a projectionscreen 51 according to another embodiment of the projection screen. Thesame components shown in FIG. 1 are denoted by the same referencenumerals in FIG. 7 and detailed description thereof is omitted here;only those components different from FIG. 1 will be describedhereinbelow. The projection screen 51 includes an optical thin film 3 ona transparent screen substrate 52 and this optical thin film 3, which iscomposed of dielectric multilayers, serves as a band-pass filter. On theoptical thin film 3, a light diffusion layer 4 is disposed and aprotective film 5 is formed on top of the light diffusion layer 4. Alight absorption layer 53 composed of a black-coated film is formed onthe bottom face of the screen substrate 52. That is, with a projectionscreen 2, the black-coated film functions as the light absorption layer53. The black-coated film does not reflect but absorbs the light passedthrough the optical thin film 3 and the screen substrate 52, therebyenhancing the black level and improving the contrast.

[0099] In the projection screen 51, the optical thin film 3 is providedso that three-primary-color light emitted from a light source passesthrough the protective film 5 and the light diffusion layer 4 to beincident on and reflected off the optical thin film 3. This reflectedlight reenters the light diffusion layer 4 and is diffused at apredetermined ratio to be emitted as a diffusive reflection componentthrough the protective film 5. The reflected light component that is notdiffused at the light diffusion layer 4 passes through the protectivefilm 5 to be emitted as a specular reflection component. The light thatis not reflected at the optical thin film 3 passes through the screensubstrate 52 to be absorbed in the light absorption layer 53 composed ofthe black-coated film. Thus, the reflected light from the projectionscreen 1 is composed of the specular reflection component and thediffusive reflection component of the three-primary-color light. Theviewer can perceive not only the specular reflection component but alsothe diffusive reflection component, greatly improving the field of view.Hence, the viewer can enjoy natural images. Similarly to the projectionscreen 1, the thus constructed projection screen 2 can provide a clearimage regardless of the brightness of the environment where theprojection screen is used, even in a bright environment.

[0100] The projection screen 51 described above may be manufactured asfollows.

[0101] First, the transparent screen substrate 52 is prepared as ascreen substrate and the optical thin film 3 composed of the dielectricmultilayers is formed on one surface of the screen substrate 52.

[0102] The optical thin film 3 is composed of dielectric multilayers.Specifically, as shown in FIG. 7, high-refraction layers H1-H51, whichare dielectric films composed of a high-refraction material, andlow-refraction layers L1-L50, which are dielectric films composed of alow-refraction material, are alternately laminated by AC sputtering toform a total of one hundred and one laminated layers of the optical thinfilm 3. At the formation of the dielectric multilayers, the thickness ofthe optical thin film 3 is calculated by the simulation based on thematrix method such that the optical thin film exhibits high reflectancefor the three-primary-color light with the blue, green and redwavelengths and also exhibits high transmittance, i.e., low reflectance,for light of wavelengths other than the blue, green and red wavelengths.The thickness of each high-refraction layer H and low-refraction layer Lis determined based on this calculation to form the optical thin film 3.

[0103] The light diffusion layer 4 with arrayed beads of a predeterminedsize is formed on the thus constructed optical thin film 3 and aprotective film 5 is formed on top of the light diffusion layer 4. Onthe bottom face of the screen substrate 52, namely, on the main surfaceopposing the surface on which the optical thin film 3 is formed,black-coating is applied to form the light absorption layer 53, therebymanufacturing the projection screen 51. The light diffusion layer 4 andthe protective film 5 may be formed using any known method.

EXAMPLE

[0104] The present invention will now be described in more detail byreferring to a specific example. The present invention is not restrictedto the following example and may be modified within the scope of thepresent invention.

[0105] With the example, a projection screen according to the presentinvention was constructed as a grating projection screen with an opticalthin film functioning as a band-pass filter for narrow-band,three-primary-color light. This grating projection screen may beemployed in the above-described grating projector in FIG. 3, forexample.

[0106] A screen substrate 62 composed of black PET with a thickness of188 μm was prepared as a screen substrate and on one surface of thescreen substrate 62, an optical thin film 63 composed of dielectricmultilayers was formed, thereby completing a grating projection screen61.

[0107] The optical thin film 63 was composed of dielectric multilayers.Specifically, as shown in FIG. 8, high-refraction layers H101-H151 andlow-refraction layers L101-L150 were alternately laminated by ACsputtering to form a total of one hundred and one laminated layers ofthe optical thin film 63. The high-refraction layers H101-H151 weredielectric films composed of Nb₂O₅, which is a high-refraction material,and the low-refraction layers L101-L150 were dielectric films composedof SiO₂, which is a low-refraction material. In the example, thethickness of each layer of the optical thin film 63 was determined bysimulation based on the matrix method such that the optical thin film 63exhibited high reflectance, namely, a high reflection coefficient, forthe three-primary-color light with a blue wavelength of about 460 nm, agreen wavelength of about 520 nm, and a red wavelength of about 620 nm.The thickness of each layer is shown in Table 1. TABLE 1 LAYER MATERIALTHICKNESS H1 Nb₂O₅ 58.10 L1 SiO₂ 52.37 H2 Nb₂O₅ 7.37 L2 SiO₂ 59.39 H3Nb₂O₅ 27.24 L3 SiO₂ 20.71 H4 Nb₂O₅ 16.69 L4 SiO₂ 32.70 H5 Nb₂O₅ 25.72 L5SiO₂ 24.19 H6 Nb₂O₅ 18.55 L6 SiO₂ 37.34 H7 Nb₂O₅ 15.23 L7 SiO₂ 32.47 H8Nb₂O₅ 18.00 L8 SiO₂ 30.08 H9 Nb₂O₅ 26.90 L9 SiO₂ 25.26 H10 Nb₂O₅ 29.03L10 SiO₂ 35.72 H11 Nb₂O₅ 17.04 L11 SiO₂ 51.78 H12 Nb₂O₅ 22.29 L12 SiO₂28.42 H13 Nb₂O₅ 28.59 L13 SiO₂ 22.69 H14 Nb₂O₅ 21.62 L14 SiO₂ 39.71 H15Nb₂O₅ 9.87 L15 SiO₂ 39.31 H16 Nb₂O₅ 26.04 L16 SiO₂ 16.02 H17 Nb₂O₅ 24.13L17 SiO₂ 42.56 H18 Nb₂O₅ 17.13 L18 SiO₂ 30.78 H19 Nb₂O₅ 30.57 L19 SiO₂27.74 H20 Nb₂O₅ 15.62 L20 SiO₂ 44.34 H21 Nb₂O₅ 25.51 L21 SiO₂ 23.92 H22Nb₂O₅ 23.41 L22 SiO₂ 36.27 H23 Nb₂O₅ 16.25 L23 SiO₂ 34.01 H24 Nb₂O₅17.15 L24 SiO₂ 30.60 H25 Nb₂O₅ 26.53 L25 SiO₂ 21.38 H26 Nb₂O₅ 26.55 L26SiO₂ 39.37 H27 Nb₂O₅ 18.95 L27 SiO₂ 44.61 H28 Nb₂O₅ 23.90 L28 SiO₂ 25.88H29 Nb₂O₅ 26.39 L29 SiO₂ 25.30 H30 Nb₂O₅ 21.31 L30 SiO₂ 37.21 H31 Nb₂O₅11.22 L31 SiO₂ 35.85 H32 Nb₂O₅ 26.10 L32 SiO₂ 17.78 H33 Nb₂O₅ 19.23 L33SiO₂ 43.30 H34 Nb₂O₅ 19.41 L34 SiO₂ 25.71 H35 Nb₂O₅ 31.28 L35 SiO₂ 33.68H36 Nb₂O₅ 15.16 L36 SiO₂ 45.93 H37 Nb₂O₅ 30.31 L37 SiO₂ 18.10 H38 Nb₂O₅23.69 L38 SiO₂ 41.09 H39 Nb₂O₅ 16.80 L39 SiO₂ 41.33 H40 Nb₂O₅ 16.34 L40SiO₂ 26.99 H41 Nb₂O₅ 32.77 L41 SiO₂ 25.90 H42 Nb₂O₅ 20.98 L42 SiO₂ 42.91H43 Nb₂O₅ 18.30 L43 SiO₂ 41.13 H44 Nb₂O₅ 24.01 L44 SiO₂ 21.16 H45 Nb₂O₅22.86 L45 SiO₂ 21.12 H46 Nb₂O₅ 25.34 L46 SiO₂ 28.41 H47 Nb₂O₅ 9.11 L47SiO₂ 41.14 H48 Nb₂O₅ 20.56 L48 SiO₂ 20.37 H49 Nb₂O₅ 12.77 L49 SiO₂ 43.49H50 Nb₂O₅ 34.68 L50 SiO₂ 23.86 H51 Nb₂O₅ 31.46

[0108] The conditions for forming the optical thin film 3 are shownbelow.

[0109] Conditions for Forming the Optical Thin Film

[0110] Refractive Index of High-Refraction Layers: n_(H)=2.4065(wavelength, 405.0 nm)

[0111]  2.259 (wavelength, 546.1 nm)

[0112]  2.224 (wavelength, 632.8 nm)

[0113] Refractive Index of Low-Refraction Layers: n_(L)=1.479(wavelength, 405.0 nm)

[0114]  1.468 (wavelength, 546.1 nm)

[0115]  1.4654 (wavelength, 632.8 nm)

[0116] Number of High-Refraction Layers: 51 layers

[0117] Number of Low-Refraction Layers: 50 layers

[0118] Refractive Index of Vacuum (Air): n₀=1

[0119] Refractive Index of Screen Substrate: n_(g)=1.71

[0120] After forming the optical thin film 63, a light diffusion layer64 of arrayed beads with a diameter of 200 μm was formed on the opticalthin film 63.

[0121] The Reflectance of the thus manufactured projection screen 61 wasmeasured for wavelengths ranging from 380 nm to 780 nm. The incidentangle of light with respect to the screen was zero degrees in this case.The results are shown in FIG. 9.

[0122] As understood from FIG. 9, the projection screen 61 exhibited areflectance as high as about 90% for the three-primary-color light withthe blue wavelength of about 460 nm, the green wavelength of about 520nm, and the red wavelength of about 620 nm. The highest reflectance inother wavelength ranges was only about 30%. This showed that theprojection screen 61 selectively reflected the three-primary-color lightwith the blue wavelength of about 460 nm, the green wavelength of about520 nm, and the red wavelength of about 620 nm, and transmitted thelight in the wavelength ranges other than the wavelength ranges of thethree-primary-color light. The projection screen 61 was provided withthe optical thin film 63 and the thickness of each layer of the opticalthin film 63 was determined by simulation based on the matrix method,thus having high reflectance for the light in the particular wavelengthranges and high transmittance for the visible light other than the lightin the particular wavelength ranges.

INDUSTRIAL APPLICABILITY

[0123] A projection screen according to the present invention displaysan image by projecting light from a light source and includes an opticalthin film composed of dielectric multilayers which exhibits highreflectance for light in particular wavelength ranges and hightransmittance for at least visible light other than the light in theparticular wavelength ranges. The thickness of each of the dielectricmultilayers composing the optical thin film is determined by simulationbased on a matrix method.

[0124] Furthermore, with the method for manufacturing a projectionscreen of the present invention, a projection screen includes an opticalthin film composed of dielectric multilayers and displays an image byprojecting light from a light source. The thickness of each of thedielectric multilayers is determined by simulation based on a matrixmethod so that the dielectric multilayers exhibit high reflectance forlight in particular wavelength ranges and high transmittance for atleast visible light other than the light in the particular wavelengthranges.

[0125] The thus constructed projection screen of the present inventionprovided with the above-described optical thin film has high reflectancefor the light in the particular wavelength ranges and high transmittancefor at least the visible light excluding the light in the particularwavelength ranges.

[0126] Accordingly, this projection screen can greatly suppressreflection of extraneous light as compared to ordinary screens,resulting in higher contrast of images formed on the projection screenand reduction in projection of extraneous light, thereby achievingbright images. Hence, the projection screen of the present invention canprovide clear images regardless of the environment where the screen isused, even in a bright environment.

1. A projection screen for displaying an image by projecting light froma light source, comprising an optical thin film composed of dielectricmultilayers and having high reflectance for light in at least oneparticular wavelength range and high transmittance for at least visiblelight other than the light in said at least one particular wavelengthrange, wherein the thickness of each of the dielectric multilayerscomposing the optical thin film is determined by simulation based on amatrix method.
 2. A projection screen according to claim 1, wherein theoptical thin film is composed of the dielectric multilayers that arecomposed of alternately laminated high-refraction layers andlow-refraction layers, the thickness of each of the dielectricmultilayers being from 5 nm to 100 nm.
 3. A projection screen accordingto claim 2, wherein the high-refraction layers comprise any one ofNb₂O₅, TiO₂, and Ta₂O₅.
 4. A projection screen according to claim 2,wherein the low-refraction layers comprise any one of SiO₂ and MgF₂. 5.A projection screen according to claim 1, wherein a light diffusionlayer is disposed on an outermost layer of the optical thin film or inthe optical thin film as an interlayer.
 6. A projection screen accordingto claim 5, wherein the light diffusion layer comprises a plurality ofsublayers.
 7. A projection screen according to claim 5, wherein thelight diffusion layer comprises arrayed beads or a film having amicrolens array.
 8. A projection screen according to claim 1, whereinthe optical thin film comprises a light absorption layer for absorbingtransmitted light.
 9. A projection screen according to claim 8, whereinthe light absorption layer contains black paint.
 10. A projection screenaccording to claim 9, wherein the light absorption layer is a supportcontaining black paint.
 11. A projection screen according to claim 1,wherein a support on which the optical thin film is formed is flexible.12. A projection screen according to claim 11, wherein the supportcomprises a polymeric material.
 13. A projection screen according toclaim 12, wherein the polymeric material comprises any one ofpoly(ethylene terephthalate), poly(ethylene naphthalate), poly(ethersulfone), and polyolefin.
 14. A projection screen according to claim 1,wherein the light is laser light.
 15. A projection screen according toclaim 1, wherein said at least one particular wavelength comprises a redwavelength, a green wavelength, and a blue wavelength.
 16. A method formanufacturing a projection screen which comprises an optical thin filmcomposed of dielectric multilayers and displays an image by projectinglight from a light source, the method comprising a step of determiningthe thickness of each of the dielectric multilayers by simulation basedon a matrix method such that the optical thin film has high reflectancefor light in at least one particular wavelength range and hightransmittance for at least visible light other than the light in said atleast one particular wavelength range.
 17. A method for manufacturing aprojection screen according to claim 16, further comprising the steps offorming the optical thin film on a support which supports the opticalthin film, and forming a light diffusion layer on an outermost layer ofthe optical thin film or in the optical thin film as an interlayer. 18.A method for manufacturing a projection screen according to claim 17,wherein the support contains black paint.
 19. A method for manufacturinga projection screen according to claim 17, wherein the support is atransparent support and a light absorption layer is formed on a surfaceof the transparent support.
 20. A method for manufacturing a projectionscreen according to claim 16, wherein the optical thin film is formed byalternately laminating high-refraction layers and low-refraction layers.